Slide 1

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 2

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 3

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 4

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 5

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 6

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 7

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 8

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 9

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 10

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 11

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 12

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 13

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 14

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 15

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 16

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 17

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 18

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 19

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 20

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 21

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 22

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry


Slide 23

5-3 Medians and Altitudes of Triangles
Warm Up
1. What is the name of the point where the angle
bisectors of a triangle intersect? incenter
Find the midpoint of the segment with the
given endpoints.
2. (–1, 6) and (3, 0) (1, 3)
3. (–7, 2) and (–3, –8) (–5, –3)

4. Write an equation of the line containing the
points (3, 1) and (2, 10) in point-slope form.
y – 1 = –9(x – 3)
Holt Geometry

5-3 Medians and Altitudes of Triangles

Objectives
Apply properties of medians of a
triangle.
Apply properties of altitudes of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Vocabulary
median of a triangle
centroid of a triangle
altitude of a triangle
orthocenter of a triangle

Holt Geometry

5-3 Medians and Altitudes of Triangles
A median of a triangle is a segment whose
endpoints are a vertex of the triangle and the
midpoint of the opposite side.

Every triangle has three medians, and the medians
are concurrent.
Holt Geometry

5-3 Medians and Altitudes of Triangles
The point of concurrency of the medians of a triangle
is the centroid of the triangle . The centroid is
always inside the triangle. The centroid is also called
the center of gravity because it is the point where a
triangular region will balance.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 1A: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find LS.
Centroid Thm.
Substitute 21 for RL.

LS = 14

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 1B: Using the Centroid to Find Segment
Lengths

In ∆LMN, RL = 21 and SQ =4.
Find NQ.
Centroid Thm.
NS + SQ = NQ

Seg. Add. Post.
Substitute
Subtract

NQ for NS.
from both sides.

Substitute 4 for SQ.
12 = NQ
Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1a

In ∆JKL, ZW = 7, and LX = 8.1.
Find KW.
Centroid Thm.
Substitute 7 for ZW.
KW = 21

Holt Geometry

Multiply both sides by 3.

5-3 Medians and Altitudes of Triangles
Check It Out! Example 1b

In ∆JKL, ZW = 7, and LX = 8.1.
Find LZ.
Centroid Thm.
Substitute 8.1 for LX.
LZ = 5.4

Holt Geometry

Simplify.

5-3 Medians and Altitudes of Triangles
Example 2: Problem-Solving Application

A sculptor is shaping a
triangular piece of iron that
will balance on the point of a
cone. At what coordinates will
the triangular region balance?

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
1

Understand the Problem
The answer will be the coordinates of the
centroid of the triangle. The important
information is the location of the vertices,
A(6, 6), B(10, 7), and C(8, 2).

2

Make a Plan
The centroid of the triangle is the point of
intersection of the three medians. So write the
equations for two medians and find their point of
intersection.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
3

Solve

Let M be the midpoint of AB and N be the
midpoint of AC.

CM is vertical. Its equation is x = 8. BN has slope 1.
Its equation is y = x – 3. The coordinates of the
centroid are D(8, 5).

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 2 Continued
4

Look Back

Let L be the midpoint of BC. The equation for AL
is

Holt Geometry

, which intersects x = 8 at D(8, 5).

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2

Find the average of the x-coordinates and the
average of the y-coordinates of the vertices of
∆PQR. Make a conjecture about the centroid of a
triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 2 Continued
The x-coordinates are 0, 6 and 3. The average
is 3.
The y-coordinates are 8, 4 and 0. The average
is 4.
The x-coordinate of the centroid is the average
of the x-coordinates of the vertices of the ∆,
and the y-coordinate of the centroid is the
average of the y-coordinates of the vertices of
the ∆.

Holt Geometry

5-3 Medians and Altitudes of Triangles
An altitude of a triangle is a perpendicular segment
from a vertex to the line containing the opposite side.
Every triangle has three altitudes. An altitude can be
inside, outside, or on the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles
In ΔQRS, altitude QY is inside the triangle, but RX
and SZ are not. Notice that the lines containing the
altitudes are concurrent at P. This point of
concurrency is the orthocenter of the triangle.

Holt Geometry

5-3 Medians and Altitudes of Triangles

Helpful Hint
The height of a triangle is the length of an
altitude.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3: Finding the Orthocenter
Find the orthocenter of ∆XYZ with vertices
X(3, –2), Y(3, 6), and Z(7, 1).
Step 1 Graph the triangle.

X

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued

Step 2 Find an equation of the line containing the
altitude from Z to XY.
Since XY is vertical, the altitude is horizontal. The
line containing it must pass through Z(7, 1) so the
equation of the line is y = 1.

Holt Geometry

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 3 Find an equation of the line containing the
altitude from Y to XZ.

The slope of a line perpendicular to XZ is
line must pass through Y(3, 6).

. This

Point-slope form.
Substitute 6 for y1,
and 3 for x1.
Distribute

.

Add 6 to both sides.
Holt Geometry

for m,

5-3 Medians and Altitudes of Triangles
Example 3 Continued
Step 4 Solve the system to find the coordinates of
the orthocenter.

Substitute 1 for y.
Subtract 10 from both sides.
6.75 = x

Multiply both sides by

The coordinates of the orthocenter are (6.75, 1).
Holt Geometry

5-3 Medians and Altitudes of Triangles
Check It Out! Example 3

Show that the altitude to JK passes through
the orthocenter of ∆JKL.
An equation of the altitude to JK is

4=1+3
4=4 
Therefore, this altitude passes through the
orthocenter.
Holt Geometry